1. Field of the Invention
The present invention relates generally to video processing systems, and more specifically, to a method and system that adaptively filter video data in response to detection of noise within the data.
2. Background of the Invention
Video processing systems are in common use for professional video production and are finding increasing use in consumer applications, such as personal computer video capture devices and video recorders such as digital versatile disc (DVD) recorders.
Analog video channels, and in particular analog video channels that originate from rendered compressed video data may not have a flat frequency response, as some frequencies may be attenuated due to the channel (e.g., video interconnect cables) or due to prior digital-domain compression algorithm that was applied to the source video (e.g., MPEG2 compression). Digital sources also have the same artifacts from compression, and particularly in the professional video production environment where compressed signals may be routed, decompressed and re-compressed many times, the compression artifacts lead to increased distortion. Further, deeper compression algorithms such as MPEG4 have an increased tendency toward introducing structured distortion.
Noise present in an analog video signal includes random noise and structured noise or distortion. Structured noise or distortion, such as the above-mentioned sources of channel and compression distortion could be removed or reduced through filtering or equalization, but as the video information is not known a priori and the channel and/or compression characteristics may dynamically change, determining the proper equalization to apply a priori does not yield the best results.
In addition to yielding a video image that is distorted or includes noise, presence of the above-described noise or distortion complicates the process of encoding video data. The noise or distortion may introduce components that are not actually part of the video image or may erroneously enhance portions of a video image that cause the re-encoding process to yield a larger data stream output than would be required to encode a noise-free and distortion-free version of the video data.
Techniques that have been applied to the pre-processing of video data for encoding include coring, in which a threshold is applied to video components to remove low-level components from the video signal prior to encoding. U.S. Pat. No. 5,161,015 describes a method for image classification with control of a pair of single-band peaking filters for the purposes of mitigating encoding distortion as an alternative improvement to coring. However, the technique described therein is applied to adaptive control of a single-band peaking filter for each direction (horizontal and vertical) that is generally useful for sharpening a video display that is transmitted through a broadcast radio-frequency channel and can introduce artifacts that it would be desirable to remove.
Therefore, it would be desirable to provide a method and system for adaptively filtering video data to reduce noise and distortion. It would further be desirable to provide such adaptive filtering in a method and system having low video processing overhead.